Gas exchange in the lung occurs in the alveolar region; this is lined with an aqueous layer containing pulmonary surfactant (PS) which lowers the surface tension at the air-water interface. While inhaled air pollutants contact PS prior to reaching the underlying cells and tissues, it is not known whether the components of PS react directly with the pollutants, and whether this alters the surface tension reducing properties, or contributes to the initiation of an inflammatory response observed in a number of studies of the effects of inhaled oxidants. For example, with NIRA support, we observed the maximum changes in the chemical composition and surface pressure-area isotherms of PS from rats exposed to O3 and NO2 24 hours after the exposure, consistent with the course of an inflammatory response; this change was most closely correlated with the development of lung parenchymal lesions which were measured simultaneously, along with reflex changes in breathing patterns and particle clearance from the respiratory tract, by the Air Pollution Health Effects Laboratory at the University of California, Irvine. It is therefore proposed, through a close interplay of in vivo and in vitro studies, to address the question: Do the gaseous air pollutants O3 and NO2, and their reaction products in the atmosphere, NO3, N2O5 and HNO3, react directly with PS and could this contribute to initiation of the inflammatory response? Specifically, the aims of the proposed research are as follows: (1) To isolate PS from rats and expose it, spread as a monolayer on an aqueous subphase similar to the situation in the lung, to 0.1-10 ppm O3, NO2, N2O5 or HNO3 in air; (2) To measure the change in surface tension of the PS caused by the exposures; (3) To analyze for the reaction products using Fourier transform infrared (FTIR) and ultraviolet spectrometry, high performance liquid chromatography combined with mass spectrometry (MS) and/or fast atom bombardment MS, and gas chromatrography and combined GC-MS of the fatty acid methyl esters; (4) To develop FTIR techniques for examining changes in the PS as it sits on the alveolar surface, and (5) To apply the latter techniques to rats exposed in vivo to O3, NO2 and the combination of the two. Elucidation of the mechanisms of oxidation of PS in this work will help to elucidate whether direct chemical reaction of these air pollutants with PS occurs and if it produces free radicals or other oxidants which subsequently lead to other manifestations of the inflammatory response to inhaled oxidants, such as lung lesions.